0
$\begingroup$

I would like to know that, since stars emit a lot of photons where some of them could be producing electrons-positrons pairs, if its mass affects the calculations, and if because of this is different from calculating the mass of a planet (which don't produce high energy photons)... Are shinning objects more massive than its own particles' masses?

$\endgroup$
2
  • $\begingroup$ All the energy produced by high-energy photons emitted from the stars comes from mass within the star converted to energy in fusion reactions. $\endgroup$
    – notovny
    Oct 5 '21 at 22:38
  • 2
    $\begingroup$ You have chosen the wrong answer. $\endgroup$ Oct 6 '21 at 12:19
5
$\begingroup$

The mass of a star is determined by its gravitational effects, not by summing up the components that give rise to that gravity.

If we were to do the latter, then we would have to include all the mass and energy in the star. This would comprise of the rest mass of all particles, the kinetic energy of the particles and the energy of massless particles like photons. It also includes the negative gravitational potential energy of the star. (The latter means that a bound star has a gravitational mass that is lower than the sum of its rest mass).

This means that the energy you mention in your question is already included, since it is part of this inventory, whatever form the mass-energy takes.

$\endgroup$
2
$\begingroup$

No, when we talk of the mass of a star, we mean its Mass-Energy. That includes the rest mass of particles it is composed of plus the kinetic/heat energy of those particles in our frame of reference, plus the energy in any photons that are part of the sun minus the gravitational potential energy that binds the sun. These all combine to give the total mass of the star. And it is this mass-energy that results in the star's gravity and inertia.

So when hydrogen nuclei fuse and give out energy (in the form of photons and neutrinos) the total mass-energy is conserved. If a photon has sufficient energy to produce a pair of electron+positron, the total mass energy is conserved. And if that pair annihilate to produce photons, the mass-energy is still conserved. The total mass is still unchanged.

Note that pair production is not a significant reaction in stars, except in extremely massive stars at the end of their lives. And the loss of radiation pressure caused by pair production destabilises the star and leads almost immediately to supernova.

$\endgroup$
2

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.